Initialization should be moved in config.py for both nailgun and file config(Also don't forget register such opt). 
Should be something like:
 self.compute(opt group name here).savana_url = 'http://{0}:{1}/v1.0'.format(controller_ip, '8386) for nailgun config
and  something like:
cfg.StrOpt('savana_url',
               default='http:10.20.0.131:8386/v1.0',
               help="savana endpoint") for file config
after this use config.compute(opt_group_name).savana_url here